I made a mistake in my original post, which was spotted by Chris L T521. I do this quite often, and when someone spots my mistakes, I normally thank the person who spotted them and just go back and edit my post. (To Chris L T521: Thanks! )

Consider the following statement;
" If this statement is true, then 1= 2. " (let's call this A)

First, let's assume A to be true. on this supposition;
As statement A is true, "If statement A is true, then 1=2" is true.
and again, as statement A is trueand "if statement A is true, then 1=2" is true, we obtain 1=2.

Now we have proved that "If this statement is true, then 1=2 " is true.